One significant deficiency in the present radio systems and in those under development is the limited amount of radio resources available. The number of radio frequencies is limited and they are divided between several systems and operators. Various solutions have been introduced to solve this problem.
Prior art radio systems intended for general use are based on the circuit-switched technique. In systems implemented according to this technique a certain channel is reserved for a connection between the devices. This channel is available to the devices for the whole duration of the connection regardless of whether there is continuous traffic on the channel or not. This solution has been sufficient for systems which transmit mainly speech. As the need for telecommunications grows, transmission connections will be increasingly used for transmitting data. The traffic to be transmitted on data connections is often very bursty, i.e. at times a lot of data is transmitted, which requires high transmission capacity, whereas at times there is little traffic on the channel. For such connections packet-switched connections are a very practical solution in respect of the use of capacity. In packet-switched connections the channel is not reserved for terminals for the whole duration of the connection, but the channel is reserved only when data needs to be transmitted. Various radio systems utilizing packet-switched traffic have been developed in which at least some of the connections between terminals are established using a packet protocol. Examples of these systems are the GPRS (General Packet Radio System) and its improved version EGPRS (Enhanced General Packet Radio System).
Since data services and their need for data transmission capacity differ from one another, several systems are provided with the ability to establish connections with different capacities. In the case of typical data connections the terminal is connected to a data network via the Internet, for example. The systems are provided with a session management arrangement, which defines the connection set-up process. The data connection needed between the terminal and the network part of the system is established in the connection set-up process.
The use of radio systems for various purposes has increased significantly during the past few years and numerous services have been developed for them. This trend is expected to continue. Most of the new services do not necessarily require a connection between the terminal and the system. One reason for this is that the amount of information to be transmitted may be rather small and the connection needed for the service between the network part and the terminal does not require continuous data transmission but data is transmitted only for a short period.
In the existing systems that utilize the packet traffic, a connection is always established between the terminal and the network part of the system via the session management arrangement; only the quality and capacity of the connection may vary according to the need. This method is thus inflexible and may waste transmission capacity.